This invention relates to refractory compositions suitable for use as mortar.
By the nature of its use, a refractory mortar must exhibit good refractoriness, be susceptible to application by troweling, and have good bonding and adhesive characteristics. In addition to the aforementioned qualities, there are many applications or fields of use that require a refractory mortar to demonstrate corrosion resistance in a hostile environment such as a steel-making furnace, copper-producing furnace, or a cell for producing aluminum by electrolysis from molten salts. In applications of this kind, the mortar must be resistant to attack from the corrosive effect of a wide variety of molten salts, slags, metals, gases and vapors emanating from the molten baths, and slag residues that result as by-products from the metal-producing process.
For example, in an electrolytic process for producing aluminum, aluminum chloride is dissolved in a molten salt of higher decomposition potential as described in U.S. Pat. No. 3,822,195. The resultant salt bath is contained in an electrolytic cell and by passing current through the cell, the aluminum chloride is decomposed, liberating the chlorine as a gas and collecting the molten aluminum in the bottom of the cell. Typically, at least a portion of the cell is lined with refractory bricks or shapes known to have good corrosion resistance in the hostile environment generated in the cell. Nitride refractories, such as silicon oxynitrides, silicon nitride or compositions of silicon aluminum oxynitride having aluminum and oxygen in solid solution in silicon nitride, hereinafter referred to as SiAlON, provide the necessary refractoriness and corrosion resistance for such a use. Heretofore, no mortar has been known to bond the bricks or shapes together, and thus there has been a continuing problem of containing the molten salt, molten metal, gases and vapors in the cell without penetration through the seams between abutting bricks or shapes.
It is desirable, therefore, to provide a mortar for bonding refractory shapes or bricks together that is capable of resisting corrosive attack in a hostile environment, such as, for example, the environment within an electrolytic cell for producing aluminum from aluminum chloride.